An Australian-first study monitoring supermarket price promotions over the course of a year has found junk foods were discounted twice as often as healthy foods, and were reduced in price by almost double the amount.

The study, led by researchers at the Global Obesity Centre in Deakin’s Institute for Health Transformation, looked at the price promotions at one of Australia’s largest supermarket chains, following on from related research that found similar trends in the discounting of beverages.

It found that the proportion of products price promoted and the size of the discount was far larger for foods with a lower Health Star Rating, the government’s voluntary front-of-pack nutrition labelling system.

Senior author Associate Professor Adrian Cameron said price was a key driver when consumers made decisions about the products they bought, and his data showed supermarkets were prioritising discounts on junk food over healthy core foods.

“We already know from previous research that supermarkets disproportionately promote less healthy food in their catalogues, at checkouts and end of aisle displays,” Associate Professor Cameron said.

“What we’re showing here is that price promotions are yet another element of our food environment that drives us toward poor diets and obesity.”

Results from the Deakin study, published today in the American Journal of Public Health, showed that when it came to healthy foods from the five core food groups, an average of 15 per cent of products were put on special every week. This was compared to nearly 30 per cent of less healthy discretionary foods being price promoted over the same period.

The average size of the discount was also much greater for less healthy food (26 per cent off), than for foods from the five core food groups (15 per cent off).

Chocolate, chips, high-sugar breakfast cereal and ice cream were the most heavily price promoted categories, going on special more often and with the biggest price reductions.

“You can see the marketing emphasis placed on unhealthy foods quite starkly when you look at cereal products,” Associate Professor Cameron said.

“High-sugar cereals were on special far more often than low-sugar cereals, and the reductions were almost twice as large.”

Associate Professor Cameron said diets rich in energy-dense, nutrient-poor foods were a major contributor to poor health globally, leading to chronic health conditions such as obesity, heart disease, diabetes and several cancers.

“Most people know in general what food is good for them, but the marketing of unhealthy food pushes hard against that knowledge and is one of the reasons poor diets and obesity remain so prevalent,” he said.

“More than two-thirds of all the food we eat is bought from a supermarket, so we desperately need these stores to be encouraging healthy eating if we want to have an impact on obesity as a country.

“We’re not talking at all about limiting choice, but just placing the focus of marketing more on food that’s actually good for our bodies.”

Associate Professor Cameron said a UK study had shown that one fifth of what’s sold on price promotion is in addition to what would be sold if the promotion wasn’t in place, factoring in the substitution effect from other products not on special.

“Policies to reduce the number and size of price discounts on junk food could improve the healthiness of food purchased from supermarkets. This is particularly important in Australia where evidence shows we have one of the world’s biggest cultures of supermarket specials,” he said.

“No countries have restricted specials on less healthy food so far, but the UK government recently proposed policies to do this. It may be that government intervention is crucial so that there’s a level playing field for all retailers.”

Another recently published Deakin study monitored price promotions on drinks at Australia’s two largest supermarkets, showing that discounts were far more common and far larger for sugary drinks, compared to other beverage products.

Lead author of that study Christina Zorbas, also a researcher at Deakin’s Global Obesity Centre, said sugary drinks were the largest contributor to added sugars in Australians’ daily diets, and were therefore a key target to improve levels of overweight and obesity.

“Evidence-backed proposals like a sugar tax, which is being implemented around the world, can be easily undermined if sugary drinks continue to be discounted so heavily by supermarkets,” Ms Zorbas said.

“This shows just how important it is to think about changing things like price promotions to encourage shoppers to buy healthier drinks instead.

“Discounts on unhealthy food and drink warrant serious attention as part of a comprehensive strategy to promote healthy diets and reduce obesity.”